Combustion engines such as diesel engines, gasoline engines, and gaseous fuel-powered engines are supplied with a mixture of air and fuel for combustion within the engine that generates a mechanical power output. In order to maximize the power output generated by this combustion process, the engine is often equipped with a turbocharged air induction system. The turbocharged air induction system increases engine power by forcing more air into the combustion chambers than would otherwise be possible. This increased amount of air allows for enhanced fueling that further increases the power output of the engine.
In addition to the goal of maximizing engine power output and efficiency, it is desirable to simultaneously minimize exhaust emissions. That is, combustion engines exhaust a complex mixture of air pollutants as byproducts of the combustion process. And, due to increased attention on the environment, exhaust emission standards have become more stringent. The amount of pollutants emitted to the atmosphere from an engine can be regulated depending on the type of engine, size of engine, and/or class of engine.
One method that has been implemented by engine manufacturers to comply with the regulation of exhaust emissions includes utilizing an exhaust gas recirculating (EGR) system. EGR systems operate by recirculating a portion of the exhaust produced by the engine back to the intake of the engine to mix with fresh combustion air. The resulting mixture has a lower combustion temperature and, subsequently, produces a reduced amount of regulated pollutants.
Two types of EGR systems are commonly available, including a low-pressure system and a high-pressure system. Low-pressure EGR systems draw low-pressure exhaust from downstream of an engine's turbine, and direct the exhaust to a location within the air intake upstream of the engine's compressor. High-pressure EGR systems draw high-pressure exhaust from upstream of the engine's turbine, and direct the exhaust to a location within the air intake downstream of the engine's compressor. Although benefits can be associated with each type of system, certain drawbacks can also be inherent to each system. For example, low-pressure systems may, in some situations and applications, have difficulty providing EGR flow sufficient to adequately reduce emissions. High-pressure systems, although capable of providing greater EGR flow than low-pressure systems, may suffer from lower component life because of harsh conditions (e.g., elevated temperatures and pressures) experienced upstream of the turbine. Thus, a system is desired that provides sufficient EGR flow without adversely affecting system integrity.
U.S. Pat. No. 5,791,146 (the '146 patent) issued to Dungner on Aug. 1, 1998 discloses a turbo-charged engine having a high-pressure EGR system with a dedicated EGR turbocharger. Specifically, the engine includes divided exhaust manifolds each having an end connected to an inlet of a main turbocharger. One of the divided exhaust manifolds branches to also provide exhaust to a compressor of the dedicated EGR turbocharger. After passing through the main turbocharger, a main flow of exhaust from the engine is either directed through a turbine of the dedicated EGR turbocharger or around that turbine by way of a wastegate valve located in the main flow of exhaust. In this manner, the wastegate valve controls EGR flow. The EGR system of the '146 patent also includes a control valve located within the branch of the divided exhaust manifold to directly regulate a flow of exhaust passing to the compressor of the dedicated EGR turbocharger. By providing a high-pressure EGR system with a dedicated EGR turbocharger, the engine of the '146 patent may have high flow capacity.
Although the system of the '146 patent may have high flow capacity, components of the system may still deteriorate prematurely because of their location within the system. In particular, the location of the wastegate valve and the control valve may expose them to high temperatures, pressures, and flow rates that can cause them to fail prematurely.
The disclosed exhaust system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.